Heat exchanger

ABSTRACT

A heat exchanger is provided. The heat exchanger includes at least one fin provided with a plurality of slits and a plurality of refrigerant tubes penetrating the fin. The refrigerant tubes include at least one front line tube and at least one rear line tube having a different diameter from the front line tube with reference to a fluid flow direction. The slits include at least one front line slit and at least one rear line slit having a difference width with reference to the fluid flow direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 and 35U.S.C. 365 to Korean Patent Application No. 10-2008-0065059 (filed onJul. 4, 2008), which is hereby incorporated by reference in itsentirety.

BACKGROUND

The present disclosure relates to a heat exchanger.

Generally, a heat exchanger is designed such that an internalrefrigerant is heat-exchanged with external fluid. The heat exchangersmay be classified into fin-tube type heat exchangers and micro channeltube type heat exchangers.

The fin-tube type heat exchanger includes a plurality of fins and aplurality of refrigerant tubes penetrating the fins. The external fluid(e.g., air) flows between the fins, in the course of which the externalfluid is heat-exchanged with the refrigerant flowing along the tubes.

The refrigerant tubes may include a plurality of front line tubes and aplurality of rear line tubes to enlarge a flow area of the externalfluid. The front and rear line tubes are arranged in a zigzag pattern.

SUMMARY

The present disclosure provides a heat exchanger that can improve a heatexchange performance.

In one embodiment, a heat exchanger includes: at least one fin providedwith a plurality of slits; and a plurality of refrigerant tubespenetrating the fin; wherein, the refrigerant tubes include at least onefront line tube and at least one rear line tube having a differentdiameter from the front line tube with reference to a fluid flowdirection; and the slits include at least one front line slit and atleast one rear line slit having a difference width with reference to thefluid flow direction.

In another embodiment, a heat exchanger includes: a plurality ofrefrigerant tubes along which refrigerant flows; and at least one finthrough which the refrigerant tubes pass, wherein the refrigerant tubesinclude front and rear line tubes with reference to a fluid flowdirection; a diameter of the front line tube is less than a diameter ofthe rear line tube; and the front and rear tubes penetrate one fin.

In still another embodiment, a heat exchanger includes: a plurality ofrefrigerant tubes along which refrigerant flows; and at least one finthrough which the refrigerant tubes pass, wherein the refrigerant tubesinclude front and rear line tubes with reference to a fluid flowdirection; the fins include at least one front line fin through whichthe front line tube passes and at least one rear line fin through whichthe rear tube passes, the rear line tube being separately formed withthe front line tube; and a diameter of the front line tube is less thanthe rear line tube.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger according to a firstembodiment.

FIG. 2 is a cross-sectional view of the heat exchanger of FIG. 1.

FIG. 3 is a graph illustrating fin efficiencies of a related art heatexchanger and the heat exchanger of FIG. 1.

FIGS. 4 and 5 are graphs illustrating a heat transfer performance andpressure loss in accordance with a width of a fin.

FIG. 6 is a perspective view of a heat exchanger according to a secondembodiment.

FIG. 7 is a cross-sectional view of the heat exchanger of FIG. 7.

FIG. 8 is a cross-sectional view of a heat exchanger according to athird embodiment.

FIG. 9 is a graph illustrating a pressure loss in accordance with a rearline slit in a last line and a rear end of a fin.

FIG. 10 is a graph illustrating a pressure loss in accordance with adistance between a center of a rear line tube and an adjacent rear lineslit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings.

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is understood that other embodiments maybe utilized and that logical structural, mechanical, electrical, andchemical changes may be made without departing from the spirit or scopeof the invention. To avoid detail not necessary to enable those skilledin the art to practice the invention, the description may omit certaininformation known to those skilled in the art. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

FIG. 1 is a perspective view of a heat exchanger according to a firstembodiment and FIG. 2 is a cross-sectional view of the heat exchanger ofFIG. 1.

Referring to FIGS. 1 and 2, a heat exchanger of a first embodimentincludes a plurality of refrigerant tubes 10 along which fluid flows anda plurality of fins 20 penetrating the refrigerant tubes 10.

In more detail, the refrigerant tubes 10 include a plurality of frontline tubes 11 that are located at a front side with reference to a fluidflow direction and a plurality of rear line tubes 12 that are located ata rear side with reference to the fluid flow direction.

The front line tubes 11 are spaced apart from each other atpredetermined intervals in a perpendicular direction to the fluid flowdirection. The rear line tubes 12 are also spaced apart from each otherat predetermined intervals in the perpendicular direction (an up-downdirection in FIG. 2) to the fluid flow direction.

The front line tubes 11 and the rear line tubes 12 are arranged in azigzag pattern relative to each other. That is, each of the front linetubes 11 is located between two rear line tubes 120.

The fins 20 are spaced apart from each other at predetermined intervals.The front and rear line tubes 11 and 122 penetrate each of the fins 20.

Meanwhile, a diameter D1 of the front tube 11 is less than a diameter D2of the rear line tube 12 so that the fluid can effectively pass throughthe heat exchanger 1.

In more detail, a part of the fluid introduced from the front side ofthe front line tubes 11 into spaces between the fins 20 passes aroundthe front line tubes 11 and is then discharged to a rear side of therear line tubes 12. A part of the fluid stays at a rear side adjacent tothe front line tubes 11.

Here, the area where the fluid stays at the rear side of the front linetubes 11 is referred to as a wake area W. As an amount of the fluidstaying at the wake area W increases or the wake area W increases, thefluid cannot effectively flow.

Accordingly, in the embodiment, the front line tube 11 is designed suchthat a diameter thereof is less than a diameter of the rear line tube 12so that the amount of the fluid staying at the wake area W or the wakearea W can be reduced and thus the fluid can effectively flow.

When the airflow can be effectively realized as described above, theheat exchange between the fluid and the refrigerant can be effectivelyrealized and thus the heat exchange performance of the heat exchangercan be improved.

At this point, a ratio between the diameter D1 of the front line tube 11and the diameter D2 of the rear line tube 12 is set to satisfy thefollowing:

1:1.1˜1.5

Here, when the ratio between the diameter D1 of the front line tube 11and the diameter D2 of the rear line tube 12 is less than 1.1 (i.e.,when the diameter D1 of the front line tube 11 is almost same as thediameter D2 of the rear line tube 12), it is difficult to achieve thereduction of the amount of the fluid at the wake area W. When the ratiobetween the diameter D1 of the front line tube 11 and the diameter D2 ofthe rear line tube 12 is greater than 1.5, an amount of the refrigerantflowing along the front line tubes 11 is significantly less than theamount of the fluid flowing around the rear line tubes 12 less than 1.1and thus the heat exchange performance is significantly reduced.

Meanwhile, when a distance from a from end 20 a of the fin 20, whichinitially meets the fluid with reference to the fluid flow direction toa center of the front line tubes 11 is referred to as L1, a distancefrom a rear end 20 b of the fin 20 to a center of the rear line tube 12is referred to as L2, and a horizontal distance from the center of thefront line tubes 11 and the center of the rear line tubes 12 is referredto as R, the R and L1 is set to satisfy the following:

R/L1=2.0˜2.5

In addition, the R and L2 are set to satisfy the following:

R/L2=1.7˜2.2

Further, in order to reduce an overall size of the heat exchanger 1, theL1 is set to be less than L2 and the L1 and L2 are set to satisfy thefollowing:

L2/L=1.1˜1.5

In addition, the R, L1, and L2 are set to satisfy the following:

R=L1+L2

Accordingly, considering the overall structure of the fins 20, the frontfin may be 2L1 and the rear fin may be 2L2.

Meanwhile, the diameter D1 of the front line tube 11 and the distance L1from the front end of the fin 20 to the center of the front line tube 11are set to satisfy the following:

2L1−D1<4.5 mm

Further, the diameter D1 of the front line tube 11 may be set within arange of 4.5-5.5 mm. For example, when the diameter D1 of the front linetube 11 is 5 mm, the 2L1 may be less than 9.5 mm.

In addition, the diameter D2 of the rear line tube 12 and the distanceL2 from the rear end of the fin 20 to the center of the rear line tubesare set to satisfy the following:

2L2−D2<4.5 mm

In addition, the diameter D2 of the rear line tube 12 may be formedwithin a range of 6.5-7.5 mm. For example, when the diameter D2 is 7 mm,the 2L2 may be set to be less than 11.5 mm.

According to the above-described embodiment, since the diameter D1 ofthe front line tube 11 is set to be less than the diameter D2 of therear line tube 12, the fluid flow resistance by the front line tube 11is reduced and the wake area in rear of the front line tubes 11 isreduced. Further, as the fluid flow resistance is reduced, an amount ofthe fluid increases and the fluid flow noise can be reduced.

Further, since the distance from the front end of the fin 20 to thecenter of the front line tube 11 is less than the distance from the rearend of the fin 20 to the center of the rear line tube 12, an overallwidth of the fin is reduced and thus the heat exchanger can be formed ina more compact design.

FIG. 3 is a graph illustrating fin efficiencies of a related art heatexchanger and the heat exchanger of FIG. 1 and FIGS. 4 and 5 are graphsillustrating a heat transfer performance and pressure loss in accordancewith a width of a fin.

FIG. 4 is a graph illustrating a case when the diameter D1 of the frontline tube is, for example, 5 mm, and FIG. 5 is a graph illustrating acase when the diameter D1 of the front line tube is, for example, 7 mm.

Referring first to FIG. 3, the transverses axis represents a speed offluid and the longitudinal axis represents fin efficiency. The graph Aillustrates a test result using a heat exchanger (a width of the overallfins is 200 mm) where the diameter of the front line tube is 5 mm, thediameter of the rear line tube 7 mm, the width 2L1 of the front line fin2L1 is 9 mm, and the width 2L2 of the rear line fin is 11 mm.

The graph B illustrates a test result using a heat exchanger (a width ofthe overall fins is 22 mm) where the diameter of the front line tube is7 mm, the diameter of the rear line tube 7 mm, the width 2L1 of thefront line fin 2L1 is 11 mm, and the width 2L2 of the rear line fin is11 mm.

In the graph B, when it is assumed that the speed of the fluid is 1 m/sand the fin efficiency is 100%, it can be noted that the 2L1 is morereduced than the 2L2. In addition, in the graph A, when the diameter ofthe front line tube is more reduced than the rear line tube, it can benoted that the fin efficiency increases by 35%.

Referring to FIG. 4, when it is assumed that the pressure loss and theheat transfer performance are 100% when the width W1 of the front linefin 2L1, the heat transfer performance and the pressure loss are reducedas the width of the front line fin is gradually further reduced from 9mm. In addition, the variation of the heat transfer performance is verysmall and the pressure loss increases as the width of the front line finis gradually further increased from 9 mm.

Accordingly, when the diameter of the front line tube is 5 mm and thewidth of the front line fin is approximately 9 mm, the increase of thepressure loss can be prevented while keeping the heat transferperformance.

Referring to FIG. 5, when it is assumed that the pressure loss and theheat transfer performance are 10% when the width W2 of the rear line fin2L2 is 11 mm, the heat transfer performance and the pressure loss arereduced as the width W2 of the rear line fin is gradually furtherreduced from 11 mm and the variation of the heat transfer performance isvery small but the pressure loss is increased as the width of the rearline fin is gradually further increased from 11 mm.

Accordingly, when the diameter of the rear line tube is 7 mm and thewidth of the rear line fin is approximately 11 mm, the increase of thepressure loss can be prevented while keeping the heat transferperformance.

In conclusion, when the diameter of the front line tube is designed tobe less than the diameter of the rear line tube, the wake area in rearof the front line tube can be reduced. In addition, when the front linefin is designed to have a greater width than the rear line fin, the heattransfer performance can be kept. Therefore, the overall size of theheat exchanger can be reduced while the heat exchange performance of theheat exchanger is improved.

FIG. 6 is a perspective view of a heat exchanger according to a secondembodiment and FIG. 7 is a cross-sectional view of the heat exchanger ofFIG. 7.

Referring to FIGS. 6 and 7, a heat exchanger of a second embodimentincludes a plurality of front line tubes 11, a plurality of rear linetubes 12, a plurality of front line fins 30 through which the front linetubes 11 pass, and a plurality of rear line fins 40 through which therear line tubes 12 pass.

In more detail, the front line fins 30 and the rear line fins 40 arespaced apart from each other. That is, the front line tubes 11 and therear line tubes 12 penetrate different fins.

Further, a diameter D1 of the front line tube 11 is set to be less thana diameter D2 of the rear line tube 12. A ratio between the diameter D1and the diameter D2 are set to satisfy the following:

1:1.1˜1.5

The reason for setting the diameter of the front line tube 11 to be lessthan the diameter of the rear line tube 12 will not be illustrated as itis already described in the first embodiment.

Further, a width W1 of the front line fin 30 in a direction in parallelwith a fluid flow direction is set to be less than a width W2 of therear fin 40.

Further, a radio between the widths W1 and W2 is set to satisfy thefollowing:

1:1.1˜1.5

As described above, as the diameter of the front line tube 11 is set tobe less than the diameter of the rear line tube 12 and the width of thefront line fin 30 is set to be less than the diameter of the rear linefin 40, the heat exchanger can be more compact.

Meanwhile, the diameter D1 of the front line tube 11 and the width W1 ofthe front line fin 30 are set to satisfy the following:

1.6<W1/D1<2.2

The diameter D1 of the rear line tube 12 and the width W2 of the rearline fin 40 are set to satisfy the following:

1.4<W2/D2<2.0

Further, the diameter D1 of the front line tube 11 and the width W1 ofthe front line fin 30 are set to satisfy the following:

W1−D1<4.5 mm

Further, the diameter D1 of the front line tube 11 may be set within arange of 4.5-5.5 mm. For example, when the diameter D1 of the front linetube 11 is 5 mm, the width of the front line fin 30 will be 9.5 mm.

In addition, the diameter D2 of the rear line tube 12 and the width W2of the rear line fin 40 are set to satisfy the following:

W2−D2<4.5 mm

Further, the diameter D2 of the rear line tube 12 may be set within arange of 6.5-7.5 mm. For example, when the diameter D2 of the rear linetube 12 is 7 mm, the width of the rear line fin 40 will be less than11.5 mm.

FIG. 8 is a cross-sectional view of a heat exchanger according to athird embodiment.

The third embodiment is identical to the first embodiment except that aplurality of slits are formed on the fins. Therefore, only the featuresof the third embodiment will be described hereinafter.

Referring to FIG. 8, a heat exchanger of this embodiment includes aplurality of front line tubes 11, a plurality of rear line tubes 12, anda plurality of fins 50 through which the front and rear line tubes 11and 12 pass.

The fin 50 includes a front line slit portion formed between the frontline tubes 11 with reference to a length direction (a perpendiculardirection to a fluid flow direction, hereinafter, an up-down directionin FIG. 8) of the fin 50 and a rear line slit portion formed between therear line tubes 12.

In more detail, the front line slit portion includes a plurality offront line slits 51 that are arranged in series in a direction inparallel with the fluid flow direction. The front line slits 51 may beformed in two or more lines. For example, the slits 51 are arranged infour lines in FIG. 8.

The rear line slit portion includes a plurality of rear line slits 52that are arranged in series in a direction in parallel with the fluidflow line. The rear line slits 52 may be arrange in three or more lines.In FIG. 8, the rear line slits 52 are arranged in, for example, fourlines.

Further, in order to form the heat exchanger in a compact design, awidth w1 of the front slit 51 is set to be same as or less than a widthw2 of the rear line slit 52. Further, the width w1 of the front lineslit 51 may be formed within a range of 0.8-1.1 mm.

In addition, the width w1 of the front line sit 51 and the width w2 ofthe rear line slit 52 are set to satisfy the following:

0.65≦w1/w2≦1

In addition, in order to form the heat exchanger in a compact design, adistance between the front line slits 51 is equal to or less than adistance d2 between the rear line slits 52.

Further, the distance between the front line slits 51 is equal to orgreater than the width w1 of the front line slit 51. The distance d2between the rear line slits 52 is equal to or greater than the width w2of the rear line slit 52.

In addition, the width w1 of the front line slit 51 and the distance d1between the front line slits 51 are set to satisfy the following:

0.7≦w1/d1≦1.0

Further, the distance d2 between the rear line slits 52 and the width w2of the rear line slit 52 are set to satisfy the following:

0.5≦w2/d2≦1.0

Further, in order to improve the heat exchange efficiency, a distance A1from a front end of the fin 50 to the front line slit 51 a in the firstline of the front line slit portion is set to satisfy the following:

0.6 mm≦A1≦1.2 mm

When considering a temperature of the fluid (air) passing through theheat exchanger, a temperature of the fluid contacting the front end ofthe fin 50 is relatively low. Accordingly, in order to allow the heatexchange at the front end of the fin 50 to be effectively realized, thefront line slits 51 a in the first line are formed to be adjacent to thefront end of the fin 51 so as to increase a heat exchange area with alow temperature fluid.

At this point, the A1 is less than 0.6 mm, it is difficult to processthe front line slit in the first line and to achieve the boundary layerdestruction effect that is a function of the slit. On the other hand,when the A1 is greater than 1.2 mm, the boundary layer of the fluid(air) is not destructed and the fluid flow distance increases.Therefore, the heat exchanger performance is deteriorated as comparedwith the case where the A1 is less than 1.2 mm.

Further, in order to allow condensed water that is generated during thepassing of the fluid through the heat exchanger to be effectivelydischarged, a distance A2 from a rear end of the fin 50 to the rear lineslit 52 a in the last line of the rear line slit portion may be formedwithin a range of 0.8-1.4 mm.

In addition, the A1 and A2 are set to satisfy the following:

0.5≦A1/A2≦0.9

Further, in order to allow the condensed water generated during the heatexchange to be effectively discharged, a distance cw from an imaginaryline connecting a center C1 of the front line tubes 11 to a center C2 ofthe rear line tubes 12 to a slit adjacent to the imaginary line is setto be greater than 0.5 mm.

That is, in FIG. 8, a distance between the front line slit in the secondline and the front line slit in the third line is formed to be equal toor greater than 1 mm and a distance between the rear line slit in thesecond line and the rear line slit in the third line is formed to beequal to or greater than 1 mm.

FIG. 9 is a graph illustrating a pressure loss in accordance with therear line slit in the last line and the rear end of the fin.

In FIG. 9, the transverse axis indicates a distance A1 (mm) between thelast line of the rear slits and the rear end of the fin and thelongitudinal line indicates the pressure loss. In addition, other testconditions are same as the graph of FIG. 4.

Here, the condensed water discharge performance varies in accordancewith the amount of the pressure loss. That is, when the condensed wateris not effectively discharged, the pressure loss increases. When thecondensed water is effectively discharged, the pressure loss is reduced.

Referring to FIG. 9, when the pressure loss is 100% when the A2 is 0.8mm, the pressure loss increases when the distance L2 is less than 0.8mm. In addition, when the distance L2 is greater than 0.8 mm, thepressure loss is reduced, in the course of which, when the distance L2is equal to or greater than 1.4 mm, the pressure loss is constantlymaintained.

Therefore, in order to reduce the size of the heat exchanger andeffectively discharge the condensed water, the A2 may be formed within arange of 0.8-1.4 mm.

FIG. 10 is a graph illustrating a pressure loss in accordance with adistance between a center of the rear line tube and the adjacent rearline slit.

In FIG. 10, the transverse line indicates two times a distance 2CW (mm)between the center of the rear line tube and the adjacent rear line slitand the longitudinal line indicates the pressure loss. Other testconditions are same as FIG. 9.

Referring to FIG. 10, when it is assumed that the pressure loss is 100%when the 2CW is 1.0 mm, the pressure loss increases when the 2CW is lessthan 1.0 mm. In addition, when the 2CW is greater than 1.0 mm, thepressure loss is reduced, in the course of which, when the 2CW is equalto and greater than 1.8 mm, the pressure loss is constantly maintained.

Therefore, in order to reduce the size of the heat exchanger andeffectively discharge the condensed water, the 2CW may be formed withina range of 1.0-1.8 mm.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A heat exchanger comprising: at least one fin provided with aplurality of slits; and a plurality of refrigerant tubes penetrating thefin; wherein, the refrigerant tubes include at least one front line tubeand at least one rear line tube having a different diameter from thefront line tube with reference to a fluid flow direction; and the slitsinclude at least one front line slit and at least one rear line slithaving a difference width with reference to the fluid flow direction. 2.The heat exchanger according to claim 1, wherein the diameter of thefront line tube is less than the diameter of the rear line tube; and thewidth of the front line slit is less than the width of the rear lineslit.
 3. The heat exchanger according to claim 2, wherein the front andrear line slits are arranged in a plurality of lines in a direction inparallel with the fluid flow direction.
 4. The heat exchanger accordingto claim 3, wherein the fins and slits are arranged to satisfy thefollowing:0.5≦A1/A2≦0.90.6 mm≦A1≦1.2 mm where, A1 is a distance from a front end of the fin tothe front line slit in a first line with reference to the fluid flowdirection; and A2 is a distance from a rear end of the fin to the rearline slit in a last line.
 5. The heat exchanger according to claim 3,wherein a distance between the front line slits is less than a distancebetween the rear line slits.
 6. The heat exchanger according to claim 3,wherein a distance between the front line slits is equal to or greaterthan a width of the front line slit; and a distance between the rearline slits is equal to or greater than a width of the rear line slit. 7.The heat exchanger according to claim 6, wherein the width of the frontline slit and the width of the rear line slit are set to satisfy thefollowing:0.8 mm≦w1≦1.1 mm0.65≦w1/w2≦1.0 where, the w1 is the width of the front line slit and thew2 is the rear line slit.
 8. The heat exchanger according to claim 6,wherein the diameter of the front line tube, the diameter of the rearline tube, the width of the front line slit, and the width of the rearline slit are set to satisfy the following:0.7≦w1/d1≦1.00.5≦w2/d2≦1.0 where, the d1 is the diameter of the front line tube, thed2 is the diameter of the rear line tube, w1 is the width of the frontline slit, and w2 is the width of the rear line slit.
 9. The heatexchanger according to claim 1, wherein a distance (cw) from animaginary line interconnecting the front line tubes or the rear linetubes to the slit adjacent to the imaginary line is equal to or greaterthan 0.5 mm.
 10. The heat exchanger according to claim 1, wherein thefront line slits are arranged in two or more lines and the rear lineslits are arranged in three or more lines.
 11. A heat exchangercomprising: a plurality of refrigerant tubes along which refrigerantflows; and at least one fin through which the refrigerant tubes pass,wherein the refrigerant tubes include front and rear line tubes withreference to a fluid flow direction; a diameter of the front line tubeis less than a diameter of the rear line tube; and the front and reartubes penetrate one fin.
 12. The heat exchanger according to claim 11,wherein a ratio between the diameter of the front line tube and thediameter of the rear line tube is 1:1.1˜1.5.
 13. The heat exchangeraccording to claim 12, wherein, when a horizontal distance from a frontend of the fin to a center of the front line tube is L1, a horizontaldistance from a rear end of the fin to a center of the rear line tube isL2, and a horizontal distance from the center of the front tube to thecenter of the rear line tube is R, a ratio between L1 and R is 1:2.0˜2.5and a ratio between L2 and R is 1:1.7˜2.2.
 14. The heat exchangeraccording to claim 12, wherein a horizontal length from a rear end ofthe fin to a center of the rear line tube is greater than a horizontaldistance from a front end of the fin to a center of the front line tube.15. The heat exchanger according to claim 12, wherein, when a horizontaldistance from a front end of the fin to a center of the front line tubeis L1 and a horizontal distance from a rear end of the fin to a centerof the rear line tube is L2, the fin and front and rear tubes arearranged to satisfy the following:2L1−D1<4.5 mm,2L2−D2<4.5 mm
 16. A heat exchanger comprising: a plurality ofrefrigerant tubes along which refrigerant flows; and at least one finthrough which the refrigerant tubes pass, wherein the refrigerant tubesinclude front and rear line tubes with reference to a fluid flowdirection; the fins include at least one front line fin through whichthe front line tube passes and at least one rear line fin through whichthe rear tube passes, the rear line tube being separately formed withthe front line tube; and a diameter of the front line tube is less thanthe rear line tube.
 17. The heat exchanger according to claim 16,wherein a ratio between the diameter of the front line tube and thediameter of the rear line tube is 1:1.1˜1.5.
 18. The heat exchangeraccording to claim 17, wherein the front and rear line tubes aredesigned to satisfy the following:1.6<W1/D1<2.21.4<W2/D2<2.0 where, the D1 is the diameter of the front line tube, theD2 is the diameter of the rear line tube, the W1 is a width of the frontline fin, and the W2 is a width of the rear line fin.
 19. The heatexchanger according to claim 17, wherein a width of the front line finis less than a width of the rear line fin.
 20. The heat exchangeraccording to claim 17, wherein a ratio between a width of the front linefin and a width of the rear line fin is 1:1.1˜1.5.